RULES FOR ASSIGNING OXIDATION NUMBERS
RULE 1: The oxidation number of any free element is 0.
Ex: H2 or P4
RULE 2: The oxidation number of a monatomic ion (Na+, Ca+2, Cl-, ....) is equal
to the charge on the ion.
Note: some ions have multiple oxidation numbers such as Fe+2 or +3
RULE 3: The oxidation number of each hydrogen ion in most compounds is +1.
Note exception: When hydrogen is a hydride, its charge is a -1.
Ex: Lithium hydride LiH
RULE 4: The oxidation number of each oxygen ion in most compounds is -2.
Ex: H2O Hydrogen ion=+1, Oxygen ion=-2
Note exception: In peroxides, oxygen charge is -1.
Peroxides take the form X2O2 such as sodium peroxide: Na2O2
RULE 5: The sum of the oxidation numbers of all the ions in a particle must equal
the apparent charge of that particle.
Ex: H2O a compound=0
ClO3- a polyatomic ion= -1
RULE 6: In compounds, the elements of Group IA, IIA, and IIIA (except Tl) have
only one oxidation number which is positive and corresponds to its group number
on the periodic table. +1, +2, and+3 respectively.
Charges
State the oxidation number by looking on the periodic table for each of the ions
that make up the compound. Don’t forget the oxidation rules. These are all
compounds so they add up to zero!!!!!
1. BaCl2
2. MgO
3. SO2
4. PH3
5. Al2O3
6. H2SO4
7. KNO3
**
**
8. AlF3
9. CaCl2
10. K2O
11. AlCl3
12. Na2O
13. FeO
Charges
State the oxidation numbers of each ion that makes up each polyatomic ion.
Don’t forget the oxidation rules. These do NOT add up to zero!!!!
1. CO3-2
2. ClO33. CrO4-2
4. CN5. Cr2O7-2
6. HCO37. HSO48. NO39. NO210. MnO411. PO4-3
12. SO4-2
13. SO3-2
14. OH15. BO3-3
16. Fe(CN)6-3
17. Fe(CN)6-4
18. HPO4-2
19. NH4+
Write the correct formula for the following binary compounds. They add up to
zero.
1. Ba +2 + S – 2 _______________
2. Na + 1 + O – 2 _________________
3. Al + 3 + Br – 1 _________________
4. K + 1 + Cl – 1 __________________
5. Sn + 4 + S – 2 __________________
6. Sn + 4 + P – 3 __________________
7. Al + 3 + F – 1 ___________________
8. Fe + 3 + F – 1 __________________
9. Zn + 2 + C – 4 __________________
10. Cu + 2 + N – 3 __________________
Write the correct formula for the following binary compounds using the periodic
table to find their charge.
1. sodium + chloride_____________________
2. calcium + oxide_______________________
3. barium + nitride_______________________
4. lithium + carbide______________________
5. aluminum + iodide_____________________
6. strontium + fluoride_____________________
7. beryllium + sulfide______________________
8. magnesium + phosphide___________________
9. hydrogen + oxide_______________________
10. carbon + chloride_______________________
Let’s try some more:
1. magnesium + nitride______________________
2. calcium + iodide________________________
3. aluminum + fluoride_______________________
4. carbon + chloride________________________
5. potassium + oxide_______________________
6. sodium + sulfide________________________
7. barium + phosphide_______________________
8. lithium + arsenide_________________________
9. beryllium + oxide_________________________
10. hydrogen + bromide________________________
11. strontium + phosphide______________________
12. carbon + nitride________________________
13. potassium + carbide_______________________
14. aluminum + sulfide_______________________
15. sodium + iodide________________________
16. magnesium + fluoride______________________
17. strontium + carbide_______________________
18. tin + oxide___________________________
19. iron + sulfide___________________________
20. aluminum + oxide__________________________
Now, you write the symbol/formula and look up the charges for the following:
Element or Ion
Symbol/Formula
Charge and Number(s)
1. aluminum
_____________
__________________
2. ammonium
_____________
__________________
3.antimony
_____________
__________________
4. barium
_____________
__________________
5. bromide
_____________
__________________
6. calcium
_____________
__________________
7. carbonate
_____________
__________________
8. chloride
_____________
__________________
9. copper(II)
_____________
__________________
10. fluoride
_____________
__________________
11. hydrogen carbonate_____________ __________________
12. hydronium
13. hydroxide
_____________
__________________
_____________
__________________
14. iron(II)
_____________
__________________
15. iron(III)
_____________
__________________
16. mercury(I)
_____________
__________________
17. hydride
_____________
__________________
18. mercury(II)
_____________
__________________
19. lead(IV)
_____________
__________________
20. nitrate
_____________
__________________
21. oxide
_____________
__________________
22. phosphate
_____________
__________________
23. potassium
_____________
__________________
24. sulfide
_____________
__________________
25. sodium
_____________
__________________
26. sulfate
_____________
__________________
27. silver
_____________
__________________ *
28. zinc
_____________
__________________ *
Now we’ll try putting some polyatomic ions into some of the compounds!!
Formula Writing
1. sodium chloride
___________________
2. ammonium hydroxide
___________________
3. calcium sulfate
___________________
4. magnesium nitrate
___________________
5. aluminum phosphate
___________________
6. zinc chloride
___________________
7. mercury (II) oxide
___________________
8. aluminum sulfate
___________________
9. silver nitrate
___________________
10. barium hydroxide
___________________
11. potassium sulfide
___________________
12. iron (II) sulfate
___________________
13. mercury (I) chloride
___________________
14. copper (II) carbonate
___________________
15. calcium acetate
___________________
16. iron (III) sulfate
___________________
17. calcium phosphate
___________________
18. zinc sulfide
19. ammonium carbonate
20. antimony (III) chloride
21. potassium oxide
22. ammonium sulfide
23. mercuric nitrate
___________________
___________________
___________________
___________________
___________________
___________________
24. iron (III) chloride
25. aluminum oxide
___________________
___________________
NAMING COMPOUNDS
Three systems of naming: New(Roman Numerals or Stock), Old(Traditional), and
Greek.
1. NEW: This system is used when there are more than one positive ion that
exists for the positive ion.(All positive ions except those in Groups IA, IIA, IIIA
and Ag, and Zn)
Ex: mercury(II) oxide
HgO
2. OLD: This system is used for five elements only: Fe, Cu, Pb, Sn, Hg
The lower of the two charges has the ending -ous
The higher of the two charges has the ending -ic
The stem for each is taken from the Latin.
Ex: Fe+2 ferrous
Cu+1 cuprous
Pb+2 plumbous
Sn+2 stannous
Hg+1 mercurous
Fe+3
Cu+2
Pb+4
Sn+4
Hg+2
ferric
cupric
plumbic
stannic
mercuric
Ex: HgO
mercuric oxide
SnF2
stannous fluoride
NOTE: Compounds named the old system can also be named the new
system BUT the opposite is not necessarily true!! Be careful.
3. GREEK: To use this system, two conditions must hold.
a) The compound must be a binary compound(a compound with only two
elements).
b) The positive ion must be located in Groups IIIA, IVA, VA, VIA or VIIA
AND to the right of the zig-zag line. Note: there are some exceptions.
Prefixes are used to name the compound.
1 mono- 2 di- 3 tri4 tetra- 5 penta- 6 hexa8 octa9 ennea- 10 deca-
7 hepta-
Ex: NO nitrogen monoxide (NOTE: mono is not used on the positive ion)
CO2 carbon dioxide
N2O3 dinitrogen trioxide
EXTRA INFO ON POLYATOMIC IONS AND NAMING:
per---ate one more oxygen that -ate
---ate MOST COMMON FORM. MEMORIZE THESE: ClO3-, NO3-, CO3-2,
SO4-2, PO4-3
---ite one less oxygen than -ate
hypo---ite two less oxygen than -ate
---ide no oxygen
EX: KClO4 potassium perchlorate
KClO3 potassium chlorate
KClO2 potassium chlorite
KClO potassium hypochlorite
KCl
potassium chloride
NAMING OF ACIDS
1. Naming of a binary acid(two elements) hydro—(stem)—ic
Ex: HF
hydrofluoric acid
HCl hydrochloric acid
2. Ternary acids(three elements
--ate ending becomes –ic
(Your --ate something --ic ky in the cafeteria)
--ite ending becomes –ous
Ex: H2SO4
H2CO2
hydrogen sulfate becomes sulfuric acid
hydrogen carbonite becomes carbonous acid
NAME
1. NaOH
FORMULA
1. sodium carbonate
2. NH4Cl
2. aluminum chlorate
3. MgCrO4
3. magnesium nitrite
4. CaCO3
4. ammonium chloride
5. FeI2
5. ferrous bicarbonate
6. Cu2O
6. carbon tetrafluoride
7. SnCl4
7. silver nitrate
8. Al(NO3)3
8. cobalt(II) phosphite
9. CCl4
9. mercury(II) sulfide
10. P2O5
10. sulfur dioxide
11. Na2PO4
11. cuprous hydroxide
12. HClO3
12. zinc nitride
13. Hg2SO4
13. potassium nitride
14. Pb(C2H3O2)2
14. plumbous fluoride
15. CO2
15. lithium phosphate
16. (NH4)3N
16. arsenic(V) oxide
17. Na2P
17. nickel(II) sulfate
18. CO
18. calcium carbonate
19. MgF2
19. lithium nitrate
20. CuCl
20. potassium phosphate
Naming and Formula Writing #2
NAME
FORMULA
1. Cr(ClO3)3
1. ferrous chlorate
2. BaSO3
2. plumbic acetate
3. Fe(NO3)2
3. barium phosphite
4. CaO
4. zinc chromate
5. CoPO4
5. copper(I) sulfate
6. CuCr2O7
6. copper(II) sulfate
7. FeBr3
7. calcium hydroxide
8. Zn(OH)2
8. potassium permanganate
9. HgCO3
9. iron(III) oxide
10. NaCl
10. iron(II) oxide
11. FeSO4
11. sodium chlorate
12. CO2
12. aluminum chloride
13. AgNO3
13. cuprous carbonate
14. PbF4
14. carbon monoxide
15. SO2
15. lithium fluoride
16. P2O5
16. barium phosphate
17. Ba(ClO3)2
17. diphosphorous trioxide
18. Cr2O3
18. nickel(II) bromide
19. NO
19. zinc nitrate
20. Li2CO3
20. magnesium nitride
Harder Naming and Fromula Writing#1
FORMULA
1. calcium chloride
13. calcium iodide
2. calcium carbonate
14. potassium fluoride
3. sodium cyanide
15. calcium hydroxide
4. magnesium oxide
16. Bismuth (III) sulfate
5. sodium fluoride
17. magnesium phosphate
6. aluminum chloride
18. mercury(II) cyanide
7. silicon(IV) oxide
19. potassium nitrate
8. zinc iodide
20. sodium hydroxide
9. cobalt(II) carbonate
21. lead(II) nitrate
10. potassium hydride
22. zinc sulfate
11. copper(II) carbonate
23. sodium sulfide
12. potassium hydroxide
24. iron(III) chloride
NAME
1. BaCl2
16. Cu(NO3)2
2. Zn(NO3)2
17. P2O5
3. CsC2H3O2
18. PCl5
4. H2S
19. SF6
5. K2CO3
20. PCl3
6. FeCl2
21. NH4NO3
7. Al(NO3)3
22. Na2SO4
8. NH4C2H3O2
23. Na2O
9. Ba(OH)2
24. Na3PO4
10. Cu(C2H3O2)2
25. NH4Cl
11. KCl
12. KBr
13. KI
14. Ca(NO3)2
26. NaCl
27. Na2SO3
28. SnCrO4
29. K2CO3
15 HgI2
30. Hg2(NO3)2
Harder Naming and Formula Writing#2
NAME
1. FeI2
11. Hg(CN)2
2. Li2Cr2O7
12. SbCl3
3. K3N
13. K2O2
4. CuSO4 3H2O
14. H3PO4
5. N2O4
15. Ca(H2PO4)2
6. NaNO2
16. Zn(ClO3)2
7. Pb(HCO3)2
17. Al2(C2O4)3
8. As4O6
18. NH4F
9. Ag2S
19. Ca(MnO4)2
10. Mg(OH)2
20. S2Cl2
FORMULA
1. tin(IV) chloride
2. potassium phosphate
3. sodium chromate
4. barium carbonate
5. potassium permanganate
6. ammonium sulfate
7. calcium chlorate
8. iodine trichloride
9. ammonium sulfite
10. dinitrogen tetraoxide
11. aluminum hydroxide
12. disulfur decafluoride
13. mercuric iodide
14. lithium peroxide
15. arsenic(III) sulfide
16. triphosphorous pentanitrate
17. ferrous phosphate
18. chromium(III) oxide
19. mercury(I) chloride
20. tin(II) bromide
21. iron(III) sulfate
22. zinc acetate
23. sodium nitrate
24. silver oxide
FORMULAS AND OXIDATION
NUMBERS
A chemical formula is a combination of symbols and numerical subscripts that
represents the composition of a compound. The symbols indicate which elements
are present and the numerical subscripts indicate the relative proportion of each
element in the compound. These proportions can be predicted using the
oxidation numbers of the elements and the charges of polyatomic ions. When
atoms acquire a charge they are called ions. Ions consisting of more than one
atom are polyatomic ions. Its oxidation number represents the apparent charge
on an atom.
It is important that all scientists use the same system for writing chemical
formulas. This helps to ensure clear and consistent transmission of information.
Therefore, the following rules should be used for writing chemical formulas.
1. In a neutral compound the sum of the oxidation numbers of the elements
and the charges on polyatomic ions in that compound must equal
zero.
2. One positive ( +) charge will neutralize one negative ( - ) charge.
3. Atoms with positive oxidation numbers or ions with positive charges are
written first.
4. When the relative proportion of an element in a compound is greater
than one, the symbol for that element must be followed by a
numerical subscript indicating its relative proportion, as in MgCl2
5. When the relative proportion of a polyatomic ion in a compound is
greater than one, the symbol for the polyatomic ion must be enclosed
by parentheses, followed by the correct numerical subscript, as in
AI2(SO4)3.
In this experiment you will use cut-out models of ions to form neutral
compounds. The correct chemical formula and name for each compound will be
determined by balancing oxidation numbers and charges.
OBJECTIVES
In this experiment, you will:
• cut out models of ions
• match the necessary
number of ions until the positive and negative oxidation numbers equal 0 •
predict the correct formulas for the compounds listed.
EQUIPMENT scissors
pencil and paper
sheet of ion models
glue stick
PROCEDURE
1. Prepare a data table as directed in the Analysis.
2. Cut out each of the “ion” squares from the sheet provided by your teacher.
3. Construct formulas for the following combina- tions of substances. For
example, the formula for a compound containing magnesium and chlorine
may be determined in the following way. Place the Mg2+ ion on a piece of
paper. Place enough CI- ions alongside the Mg2 + ion to balance the
charges. (Positive charges must equal negative charges.)
4. Predict formulas for four additional compounds using the ions listed in this
experiment. (see data table for requirements). Use references to determine if your
compounds exist.
Combining Substances:
aluminum and bromine
sodium and oxygen
iron(II) and sulfur
aluminum and nitrate ion
potassium and sulfate ion
iron(III) and chlorine
ammonium ion and sulfur
aluminum and oxygen
iron(lII) and sulfate ion
sodium and phosphate ion
ANALYSIS
Use the table provided for your data. Be sure to use enough
glue so that the ions do not fall off the chart. Use the rules listed in your
textbook for writing formulas and naming compounds.
CONCLUSIONS
1. Some compounds are described as binary com- pounds. What does this term
mean? What ending is given to the name of this type of compound? Refer
to your data table and list the formulas for any binary compounds you
have constructed.
2. Most polyatomic ions end in -ate or -ite. Name at least two which end in -ide.
(Look in your notes from class or your textbook)
3. Hydrogen peroxide (H2O2) and water (H2O) both contain the same two
elements. Using reference materials, describe their properties and uses. Use the
information on hydrogen peroxide and water, and the data from this experiment
to discuss the importance of writing correct chemical formulas.
Discussion questions:
Now, you make up a compound that fits the following criteria:
State its formula and its name.
1. Transition metal + Polyatomic anion
2. Transition metal + anion from family 15, 16, or 17
3. Cation from family 1, 2, or 13 + Polyatomic anion
4. Cation from family 1, 2, or 13 + Anion in family 15, 16, or 17
Conclusion questions 1 and 2 for the “B”
Conclusion question 3 for the “A”